9 mm Winchester Magnum & 45 Auto Magnum Cartridges:

The 9mm Winchester Magnum ( 9x29 mm) was developed in the late 1970s to match the .357 Magnum revolver performance, - pushing a 115 grain pill at 1,450 feet per second ..

9 MM Winchester Magnum with a Standard 9x19mm NATO.

and the .45 Winchester Magnum was a strengthened & lengthened souped-up ,45 ACP that might throw a 230 grain JHP bullet at a hot 1,600 ft. per sec.

.45 Winchester Magnum with a Standard .45 ACP.

Now my guess would be that both these Magnum cartridges needed strengthened & enlarged pistols to feed, contain and cope with the much increased power and velocity levels..

- Then the guns needed to cope were necessarily bulky, heavy and expensive - and maybe a little "clunky"?

The Wildeye, Thompson Centre and Automag III were specialist guns sized to be practical for sporting purposes but not for the typical US buyer (and that's where the market is!) - who seem to be mostly focused on self defense and "carry".

Automag III

Perhaps both cartridges were too extremely 'magnumized' for their own good - too specialised ? .. Maybe a more moderate version that might have been shootable in near standard sized auto-pistols of the day would have worked?

- The 10 MM Auto has almost made it as an 'established' cartridge.

I guess both cartridges would have been really LOUD pigs to blast-off ... maybe?